The organisers of the Giro d'Italia were forced to cancel the toughest stage of the race over the two highest mountains owing to snow and were left fighting to save what was planned to be the climax of the tour on Saturday.

And proving that trouble comes in threes, the former winner Danilo Di Luca, who had been one of the livelier performers in the 17 stages since the race left Naples, was announced positive for the blood booster erythropoietin and faces a life ban.

Di Luca has been suspended pending analysis of his B sample and has been sacked by his team, Vini Fantini. The Italian, winner of the Giro in 2007, was banned for three months that season over a doping inquiry and has a history of doping imbroglios, most notably a two-year ban for the EPO derivative Cera in 2009. He had been without a team for this season until he signed late in the spring with Fantini, a relatively low-budget squad to whom he brought a personal sponsor.

Having returned to racing only on 27 April, Di Luca had raised eyebrows by racing aggressively at the Giro, a surprise for a man with only one day of competition in his legs before the event. Testers targeted him for a test on 29 April which turned up the positive sample.

Even Lance Armstrong was surprised, tweeting: "Knowing I have 0 cred on the doping issue – I still can't help but think, 'really Di Luca? Are you that f—ing stupid??'".

Valentino Sciotti, the Vini Fantini team director, said: "I wanted and believed in the man and the rider, and it's only right that I take all the blame because I made a mistake. Maybe I made a mistake in believing that someone can redeem themselves after an error and not make one again. Maybe I made a mistake in wanting to help someone who I saw in difficulty."

It is the second doping case from this year's race, after the French rider Sylvain Georges tested positive for the banned stimulant heptaminol in a urine sample following the seventh stage. The 28-year-old AG2R-La Mondiale rider was immediately withdrawn from the race.

Heavy snow and low temperatures prompted an amended route for Friday's stage 19, but even the lower-altitude passes on the new route were made impassable overnight. This was the first time since 1989 that an entire stage had been cancelled owing to the weather.

A radically altered route for Saturday's penultimate stage to the Tre Cime di Lavaredo summit was announced, with three of the four passes on the schedule cut out of the route.

The decision means that Mark Cavendish's personal goal of winning the red points jersey is within his reach, as there is little chance that his main rival Cadel Evans can gain enough of a margin on Saturday.